The invention will be described for illustration in the context of a robotic arc-welding, seam tracking system. However, the system is equally effective for guidance and control of any type of industrial robot which is required to locate and/or track indicia on a workpiece. The indicia may be in the form of a dot, a hole, a line, a groove, a seam or a similarly indicated path or point.
The use of optically controlled seam trackers in conjunction with robotic welders has been extensive in recent years. Examples of such systems are found in the following U.S. Patents: Taft et al U.S. Pat. No. 4,833,381 issued May 23, 1989; Gordon U.S. Pat. No. 4,831,233 issued May 16, 1989; Richardson U.S. Pat. No. 4,737,614 issued Apr. 12, 1988; Shibata et al U.S. Pat. No. 4,667,082 issued May 19, 1987; Polick et al U.S. Pat. No. 4,590,356 issued May 20, 1986; Smith et al U.S. Pat. No. 4,567,348 issued Jan. 28, 1986; and Richardson U.S. Pat. No. 4,501,950 issued Feb. 26, 1985.
Review of previous systems reveals critical shortcomings in the systems capabilities to provide an effective and inexpensive means of providing three dimensional guidance for robotic welding apparatus. It will be noted that these devices are not capable of providing a usable 3-D optical image of the seam unless the seam is grooved or spaced.
By use of the stereo vision concept with a single camera the present invention provides features not possible with the above listed or any known prior art. In addition to the ability of the present invention to track accurately, the stereo vision concept permits precise quantitative three dimensional control of an industrial robot. Use of a single camera, rather than two cameras, not only halves the camera costs but greatly simplifies the system electronics and reduces the size of the program software.